1. Field of the Invention
The invention relates to optoelectronic circuits for simultaneous transmitting and receiving operation in a wavelength multiplex process, in a structure in which the relative position of active circuit components determines their operating mode. Single-stage as well as multi-stage circuits with a light waveguide arrangement and light signal detectors and light signal sources as active circuit elements for bidirectional and unidirectional transmitting and receiving operations will be disclosed. The circuits may be structured as integrated or hybrid circuits.
2. Discussion of the Prior Art
A bidirectional optical transmitting and receiving device is known from British patent specification GB-A-2,241,130 provided with an optical duplexer having a waveguide coupling device structured as a quadruple gate. Two gates of the quadruple gate at the same connection side are connected to the active circuit components for transmitting and receiving. The other two gates at the other connection side lead, on the one hand, to an external waveguide and, on the other hand, to a phase shifter. For the reduction of interfering effects between transmitting and receiving components, complementary signals are used which are guided through the actually unnecessary fourth gate and are made available by reflection at a reflecting surface and at the phase shifter.
The state of the art from which the invention is proceeding, is known from Ragdale, C. M., Reid, T. J., Reid D. C. J., Carter, A. C.: Integrated three channel laser and optical multiplexer for narrowband wavelength division multiplexing, Electronics Letters 1994, Vol. 30, No. 11. A wavelength multiplexer is described there which permits unidirectional multi-channel data transmission through a light waveguide. In this respect, the following details are set forth in greater detail:
The wavelength multiplexer is provided with three lasers each of which energizes a transmission channel. The separation between the wavelengths of the lasers, i.e. the channel spacing, amounts to about 5 nm.
The lasers are connected to a signal output by way of several 3 dB couplers, light waveguides and wavelength-selective grating reflectors, at which output the light signals emitted by the lasers are coupled to an external light waveguide. The multiplexer is structured as an optoelectronic integrated circuit, i.e. all structural components are integrated on a chip.
Each 3 dB coupler is connected with four branches of light waveguides, the branches being positioned in opposite pairs. Thus, the first branch and the second branch are arranged opposite the third and fourth branches, respectively.
The first laser of wavelength .lambda..sub.1 is connected to the first branch of the 3 dB coupler. Hence, 50% of the light signals emitted by the first laser are coupled into each of the third and fourth branches of the 3 dB coupler. A wavelength-selective grating reflector reflecting light of wavelength .lambda..sub.1 and being transparent to light of any other wavelength, is arranged in each of the third and fourth branches of the first 3 dB coupler. Thus, the light emitted by the first laser is reflected by the grating reflectors and passes through, or transverses, the coupler again in the opposite direction. The light emitted by the first laser is coupled almost entirely into the second branch to which the signal output of the multiplexer is connected. Since the first 3 dB coupler couples almost the entire light reflected at the grating reflectors into the second branch, not only is interference of the laser by light returning to the first branch prevented but the efficiency during transmission is also improved.
The first laser, the first 3 dB coupler and the first wavelength-selective grating reflector are part of a first stage which energizes the first channel with wavelength .lambda..sub.1. Following this first stage, there is arranged an analogously constructed second stage, the laser of the second stage transmitting light of wavelength .lambda..sub.2 and the wavelength-selective grating reflector of the second stage reflecting light of wavelength .lambda..sub.2.
The second branch of the second stage is connected by a further 3 dB coupler to the third and fourth branches of the first 3 dB coupler of the first stage. The light emitted by the laser of the second stage is therefore coupled at 50% each into the third and fourth branch of the first 3 dB coupler of the second stage, by the 3 dB coupler of the second stage. It is there reflected at the wavelength-selective grating reflectors and coupled almost entirely into the second branch of the second stage. The 3 dB coupler arranged between the first and second stages couples 50% of the light emitted by the second stage into the third and fourth branches, respectively, of the first 3 dB coupler of the first stage. There, the light from the second stage passes through the wavelength-selective grating reflectors since these are tuned to the first wavelength .lambda..sub.1, and is coupled almost entirely into the second branch of the first stage by the first 3 dB coupler of the first stage. It is thus fed to the signal output of the multiplexer.
A fourth 3 dB coupler is arranged following the second stage, the third and fourth branches of this fourth 3 dB coupler being respectively connected to the third and fourth branch of the 3 dB coupler of the second stage. A third laser emitting light of wavelength .lambda..sub.3 is connected to the first branch of the fourth 3 dB coupler. Hence, the light emitted by the third laser passes through the two wavelength-selective grating reflectors of the first and second stages, respectively, and is in the end coupled at the signal output into the external light waveguide.
Accordingly, the multiplexer is constructed of three stages, each stage energizing one channel with light signals. This described wavelength multiplexer allows unidirectional multi-channel date transmission by way of a light waveguide, that is to say it allows multi-channel transmission. The arrangement may also be constructed and operated as a wavelength demultiplexer. The arrangement does not, however, permit simultaneous operation as a transmitter and as a receiver, even, if necessary, by way of a single light waveguide.